1. Field of the Invention
The present invention relates to an image forming method that performs image formation by an ink jet head that uses a plurality of line heads containing therein ink of secondary chromatic colors.
2. Background Art
In ink jet printers, there are a printer in which uses a short serial head and performs recording while scanning the head in the width direction of a recording medium, and a printer using a line head in which recording elements are arranged over the entire areas in the width direction intersecting the transport direction of a recording medium. In the printer using such a line head, it is not necessary to equip a transport system such as a carriage for scanning the short serial head, and control related to the movement of the carriage and complicated scanning control of the recording medium are not necessary. Furthermore, since only the recording medium is moved, it is possible to achieve higher recording speed than the printer using the serial head.
In an ink jet printer using such a line head, generally, since the nozzles have to cover the entire width of the recording medium, the number of nozzles is inevitably much more than that of the serial head, and therefore, the possibility of occurrence of a non-ejection nozzle is higher than that of a printer using the serial head. When such a non-ejection nozzle is found, stripe unevenness is formed in the direction of the relative movement of the head on the recording medium. However, in the case of the line head, from the viewpoint of efficiency, since all the colors are usually rendered during one transport, a compensation method that compensates or obviates the stripe unevenness by using inks of the same color in a plurality of scanning operations, as used in the printer using the serial head is not usable.
For this reason, in the known ink jet printers using the line head, the following compensation method is employed:
(1) An ink of a different color at the same position as the non-ejection nozzle is substituted (referred to as “different color compensation”);
(2) The amount of inks of the same color of a nozzle adjacent to the non-ejection nozzle is increased (referred to as “adjacent compensation”); and
(3) A combination of the above compensation methods.
According to a different color compensation technique (JP-A-2002-019101 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)) in the known non-ejection correction method, occurrence of the non-ejection nozzle is compensated by using the method (3).
According to a recent ink jet recording technique, in order to expand a color reproduction range, a multi-color printing with five to seven colors is used in which inks of secondary chromatic colors of red (R), green (G), and blue (B) are added in a normal four-color (CMYK) printing, which uses inks of primary chromatic colors of cyan (C), magenta (M), and yellow (Y) and an ink of black (K).
As an example of a separation technique that uses such inks of secondary chromatic colors, JP-A-2004-209900 discloses a technique in which the secondary chromatic colors are used only to expand the color reproduction range. In the disclosed technique, there is a possibility that the above-described non-ejection nozzle is found in an ink jet printer using the line head, which may therefore cause stripe unevenness. Therefore, a non-ejection correction method is required which can be optimally used when a set of multi-color inks including secondary chromatic colors is used.
Although a non-ejection correction method disclosed in JP-A-2002-019101 is directed to a technique that makes stripe unevenness less conspicuous, the method is base on the assumption that the ink set is composed of inks of colors C, M, Y, and K (including light primary chromatic colors Lc and Lm). Moreover, since a multi-color ink set containing secondary chromatic colors of R, G, and B is composed of much more colors, the pattern of the stripe unevenness may become more complex; however, JP-A-2002-019101 does not disclose any construction corresponding to this, and moreover, it cannot be said to be the optimal one.